Chair mechanism



FIG. 1 is a front view and showing one representation of the design in its environment;

FIG. 2 is a front view of the representation of the design shown in FIG. 1;

FIG. 3 is a right side view of the representation of the design shown in FIG. 1;

FIG. 4 is a left side view of the representation of the design shown in FIG. 1;

FIG. 5 is a rear view of the representation of the design shown in FIG. 1; and,

FIG. 6 is a bottom plan view of the representation of the design shown in FIG. 1.

The portion of the chair shown in dashed lines does not form part of the claimed design. 

The ornamental design for a chair mechanism, as shown and described. 